HI there, im not sure whether this is the correct place to post,

im looking for some advice from those who once undergone ACL surgery and recover from it...im currently 6 moths post operation, and just started cycling (mountainbiking) for past 2 months with knee braces to aid...

but during those cycling session, muscle soreness, pain kicking in, hindering me from fully using my strength when pedalling...

so im looking for some advise on what exercise do i need to do to gain my knee strength back

Why not do swim and phisio in gym 1st?
Its less harm to ur weak muscle and acl..

my area doesnt have any pool accessible at night which when i will be free to do anything....currently doing home exercise, but i think its not helping since i tend to get bored quite fast unless there is someone to guide me

Better find a physiotherapist or a sport therapist to help you get back in shape.
Normally after ACL recon, there is a certain protocol used by the physio or the sport therapist to train you back. The rehabilitation process usually take 6 months (fastest) to recover back.
Don't do your own exercise if you are uncertain of it because ACL might torn again if your ligament still weak if didn't strengthen well...